Solid waste materials of the type typified by municipal waste have traditionally presented problems of disposal, and these problems have become increasingly critical in recent years as a result of not only a rapidly increasing population, but also the compounding difficulty of the drastic increase in per capita production of solid waste. In addition, there has been a recent notable change in the character, or composition, of municipal waste, due primarily to the supplanting of metal, wood and glass as packaging materials by paper and plastic. For example, a recent industry-sponsored survey reported that collected waste in the United States in 1970 included six billion pounds of plastic, of which approximately 37% was film.
Conventionally, solid waste has been disposed of primarily by incineration and land fill, and the replacement of inorganic packaging materials by paper and plastic has resulted in the favoring of incineration over land fill. Over the last several years, however, the public has become increasingly aware of solid waste as a source of atmospheric pollution as well as the prime example of dissipation of natural resources. This has led to a growing demand by both government and the public that wherever possible, recycling should be employed to accomplish the dual results of reduction of the pollution problem and conservation of natural resources.
There is presently a growing interest in the area of generic segregating, blending, and the use of waste plastic. Yet in spite of the increasing serious shortages in virgin material for the production of plastic, there has been insignificant activity in the development of techniques for separating plastics from the other contaminants present in solid waste. Salvage from municipal solid waste has thus far been practiced only in isolated cases, with the great majority of the plastic discarded in municipal solid waste being incinerated or buried.
As further background of the invention, a report by the U.S. Department of H.E.W. as recently as 1968 gave the typical composition of municipal refuse as comprising 5% plastics on a bone dry basis, which translated into 6.6% of the total organic constituents, the great majority of this plastic consisting of polyethylene, polyvinyl chloride and polystyrene. This has been substantially confirmed by the experience of the assignee of this application, during the course of operating a new municipal waste recycling plant in Franklin, Ohio since mid-1971. The present invention grew out of the belief that this large percentage of plastic justified the development of a successful method of separating it from the other organic constituents of municipal waste.